Highly elastically or plastically stretchable self-adhesive tapes which can be detached again without residue or destruction by stretching in the bonding plane are known, for example, from U.S. Pat. No. 4,024,312 A, DE 33 31 016 C2, WO 92/11332 A1, WO 92/11333 A1, DE 42 22 849 A1, WO 95/06691 A1, DE 195 31 696 A1, DE 196 26 870 A1, DE 196 49 727 A1, DE 196 49 728 A1, DE 196 49 729 A1, DE 197 08 364 A1, DE 197 20 145 A1, DE 198 20 858 A1, WO 99/37729 A1 and DE 100 03 318 A1 and are referred to inter alia below as strippable self-adhesive tapes.
Strippable self-adhesive tapes of this kind are frequently used in the form of single- or double-sided PSA film strips, which preferably have a nonadhesive grip region from which the detachment operation is initiated. Particular applications of such self-adhesive tapes can be found, inter alia, in DE 42 33 872 A1, DE 195 11 288 A1, U.S. Pat. No. 5,507,464 A, U.S. Pat. No. 5,672,402 A and WO 94/21157 A1. Specific embodiments are also described in DE 44 28 587 A1, DE 44 31 914 A1, WO 97/07172 A1, DE 196 27 400 A1, WO 98/03601 A1 and DE 196 49 636 A1, DE 197 20 526 A1, DE 197 23 177 A1, DE 197 23 198 A1, DE 197 26 375 A1, DE 197 56 084 A1, DE 197 56 816 A1, DE 198 42 864 A1, DE 198 42 865 A1, WO 99/31193 A1, WO 99/37729 A1, WO 99/63018 A1, WO 00/12644 A1, and DE 199 38 693 A1.
Preferred fields of use of the above-mentioned strippable adhesive film strips include in particular the residuelessly and nondestructively redetachable fixing of light to moderately heavy articles in the home, workplace and office segments. In these applications they replace conventional fastenings means, such as drawing pins, roundhead needles, thumbtacks, nails, screws, conventional self-adhesive tapes and liquid adhesives, for example. Key to the successful use of the above-mentioned adhesive film strips is not only the quick and easy bonding and the secure hold they provide for the envisaged period of bonding but also the possibility for residueless and nondestructive redetachment of bonded articles. It should be borne in mind in particular here that the adhesive strips must function on a large number of substrates in order to be able to serve as a universal fixing means in the home, workplace, and office segments.
Despite the fact that the patent literature cited above describes a broad range of pressure sensitive adhesives for use in strippable self-adhesive tapes, commercial products currently on the market (for example, tesa® Powerstrips® from Beiersdorf AG, 3 M Comand® Adhesive strips from 3M, and Plastofix® Formule Force 1000 adhesive strips from Plasto S.A.) all have pressure sensitive adhesives based on styrene block copolymers, generally with unsaturated polydiene blocks in the elastomer block. Typically, use is made of linear or radial block copolymers based on polystyrene blocks and polybutadiene blocks and/or polyisoprene blocks; i.e., for example, radial styrene-butadiene (SB)n and/or linear styrene-butadiene-styrene (SBS) and/or linear styrene-isoprene-styrene (SIS) block copolymers. Advantages of the aforementioned styrene block copolymer based pressure sensitive adhesives for use in strippable self-adhesive tapes are, for example, the very high bond strengths which can be achieved with them (owing, inter alia, to the simultaneous realization of very high cohesion and very high bond strengths), pronounced reduction of tack during stretching detachment (which greatly facilitates, if not indeed being a precondition for, the operation of detachment), and a very high tensile strength, which is essential in particular for an operation of detachment with no tearing.
The products available on the market, all of which utilize pressure sensitive adhesives based on styrene block copolymers, exhibit weaknesses in bond strength at temperatures above 50° C. As a result of softening of the hard phases, which consist principally of polystyrene (block polystyrene domains), the PSA strips fail cohesively particularly when used to bond moderately heavy articles.
Failure of the bond occurs to a much greater extent in the case of a tip shearing load (where a torque is active, such as in the case of the bonding of a hook, for example) than in the case of a simple shearing load.
It is an object of the invention, therefore, to provide an improved pressure sensitive adhesive based on styrene block copolymers for pressure sensitive adhesive film strips which can be redetached without residue or destruction by stretching in the direction of the bonding plane and which exhibit a good bond strength even at elevated temperature.